Amplifying system



. 1,524,581 J. SCOTT-TAGGART AMFLIFYING SYSTEM Original Filed se a; 29,

I v INVENTOR eatenieea 2 was.

JOHN seorr-TAeGAri'r, or ILFORD, ENGLA D, ASSIGNOR TO ALFnEn ERNEST WHITE,

- or LoNnoN, ENGLAND. I

AMPLIFY ING SYSTEM.

Original application filed September 29, 1924, Serial No. 740,496. Divided and this application filed December 29, 1924..

there are employed two or more stagesrof high-frequency amplification involving the use of two or more circuits tuned to the incoming frequency, and arranged so that each of two anode circuits has a tuned circuit associated with it either by coupling.

or direct connection, undesirable reactions or self-oscillations will very likely occur. This tendency toward undesirable reactions is due largely to capacity coupling in the valves themselves.

It has been proposed to counteract the tendency to self-oscillation of a single valve amplifier due to inherent capacity coupling between the electrodes ofthe valve by the use of a condenser connected so as to produce a reverse reaction effect, but when a plurality of stages of high-frequency amplification is involved, it has not hitherto been contemplated, so far as I am aware, that similar means could be successfully applied to said systems, owing to the relatively greater dilliculties involved with each successive stage of amplification. 'I have found that by the suitable use of con densers connected to proper terminals of associated inductance coils in various stages,

it is possible to neutralize this natural reaction effect and thereby insure the stability of the amplifier,

Accordingly, the invention in part consists of a high-frequency amplifier [in which the currents are amplified by v a pluralityof stages of amplification involving a plurality of circuits, one or more condensers being connected so as to produce a reverse reac: tion effect to neutralize thetendency of the amplifier to generateoscillations.

A further feature of the'invention con- Serial No. 758,648.

sists in a wireless receiver in which the in= coming high-frequency currents are amplified by a plurality" of valves 1n cascade s'coupled together, by the aid of circuits sub stantially tuned to the incoming frequency, and 1n which condensers are used, in the case of at least two valves, to feedback output currents of the valves to their rcspective input circuits so as to neutralize the natural reaction effects in the valves concerned. I

The invention also provides an amplifying system usi a thermionic valve in which the natural coupling capacitv between the anode and the grid electrode and their respective circuits is supplemented by a condenser, another and distinct condenser being employed tobalance out the reaction effects. i

Other features of the invention and the methods for carrying the same into efi'ect will be seen from a consideration of preferred embodiments of the same as disclosed in the accompanying drawings, and appended claims.

This application is a division of the application for United States Letters Patent of John Scott-Taggart, Serial No. 740,496, filed September 29, 1924.

Fig. 1 represents a three-valve receiver in which two valves are utilized as high frequency amplifiers coupled by tuned highfrequency transformers, the undesirable reaction effects ,due to the inter-electrode ca-' pacity coupling in the valves being neutralized by means of this invention.

Fig. 2 shows a circuit diagram of a three valve receiver employing two stages of condenser-coupled high-frequency amplification with the present invention employed to balance out the undesired reaction efiects due to the inter-electrode capacity coupling in the valves. C Referring to Fig. 1, it will. be seen tha the thermionic valves V, and V serve as high frequency amplifiers, and the thermionic valves V functions as a. detector. The antenna circuit L, and vC can be tuned to the incoming signal while-thesecondary inductanceIlL and thGrvariable condenser C serve to tune-the input :circuitof the thermionic valve; V1.1 in resonance "with the antenna circuit. The anode or output cirmary inductance L The connection to the inductance L and the variable condenser- G The grid of the valve V is connected to a point between variable condensers C and C; while the high-tension battery B is connected to the filament circuit of the valve V and thence to-a point on the priprimary inductance L need not be fixed, but may be variably'connected to any of the points intermediate the extremities of that coil. Condenser C is a supplemental capacity connected across the grid electrode and the anode of valve V in order to increase the natural grid-to-anode capacity existing in valve V and between the circuits connected to these electrodes, in order that the resultant capacity may be increased to a practicable value. A discussion of the operation ofthis supplemental capacity and a statement of the advantages to be derived therefrom will be found in the applicants mentioned copending ap lication.

The tuned circuit L 8 in the input or grid circuit of the valve V is coupled to the primary inductance L of the output circuit of the valve V The anode or output circuit of the valve V is tuned by means of the primary inductance L shunted by the variable condenser C The variable condensers C, and C are connected across the terminals of the condenser C of the primary inductance L in the same manner as condensers C and C The grid of the.

valve V is connected to a point between the condensers (J and C The valve V in the same mannerxas the valve V has .an anode circuit provided with an adjustable connection to the high tension battery 13 by means of a variable tap engaging the windings of the inductance L The input circuit of the detector valve V has a secondary inductance L coupled to the inductance L of the output circuit of the preceding valve and hasa variable condenser CD which functions to tune valve V to the incoming signal. The usual grid condenser C shunted by a grid leak R is provided in the grid or input circuit of the detector valve V while the anode or output circuit of this valve includes'the telephones T shunted by a bypass condenser C In the present arrangement the condenser '0 neutra izes an reaction currents which normally would ow through the coupling capacity existin between the anode and the grid electrode 0 the valve V and the supplemental condenser C while the condenser 0 neutralizes the capacity coupling existing between the anode and grid electrode the output circuit of the valve V mac-cs1 of the valve V and its supplemental condenser C It will be noted that the accumulator B supplies the filamentsof the valves witli heatinflurrent through the -rheostats R an R5.

Fig. 2 shows a modified circuit diagram of a receiver which is substantially similar to the circuit arrangement shown in Fig. 1 except that the various valves-are coupled capacitatively rather than inductively. The antenna circuit is tuned and the input cir cuit of the valve V is likewise tuned, as in the preceding arrangement. The anode circuit of the valve V includes inductance L and the high tension battery B while variable condenser C and inductance L are connected in series around inductance L The supplemental variable condenser C is connected between the grid electrode and anode of valve V to supplement the inter-electrode capacity existing between these elements and the circuits connected thereto, and the variable condenser C has I one terminal connected to a point between the variable condenser C and the inductance L and has its other terminal connected to a conductor leading to the grid electrode" of valve V Thus the variable condenser C 'supplements the inter-electrode capacity, while thevariable condenser C functions to neutralize any reaction currents which would otherwise pass through the inter-electrode capacity of valve N and its suppelemental condenser C The variable condenser C and the resistance R, couple the output or anode circuit of valve V to the inputcircuit of valve V The anode in the output circuit of the valve V is associated with a net-work including a primary inductance L a secondary in- I ductance L connected by means of a variable condenser in the same arrangement as In this instance'also the variable condenser C connected between the grid electrode and anode of the valve V supplements the inter-electrode capacity of this valve whilethe variable condenser C is connected to the network last mentioned in such a manner as to neutralize any reaction effects due to the inter-electrode capacity of the valve V and its supplemental condenser C The fixed condenser 0 and'the resistance R serve to connect the anode or output circuit of the valve V to the grid. of the detector valve V The telephones T together with the high tension battery B are connected in the anode circuit of this last mentioned valve. 7

While the high tension battery B is connected to the midpoint of the inductance represented at L L and L L it will be understood that this connection ma be made variable as in the arrangement own in Fig. 1.

Iclaim: r 1. In an amplifying system, a series .of

valves arranged in cascade, each valvebeing provided with a tuned input circuit and an output circuit, whereby inherent capacity coupling may exist, a condenser connected between the input l circuit andwthe output circuit of each stage to supplement said: in-' herent capacity, another condenser coupling tioned condensers. I

'2. In an amplifying system, a plurality of amplifying'stages, each of said stages being provided with a tuned input circuit and a tuned output circuit whereby inherent capacity couplingmay exist, a condenser connected between the input circuit and the output circuit of each stage to supplement 1 the inherent. capacity coupling, a condenser.

' coupling adjacent stages, and means includmg other capacities for neutralizing said-inherent capacities of said Stages and said first-mentioned condensers. I v

3. In an amplifier, a'valve provided with a filament, a grid electrode and an anode,

a tuned input circuit-connected between said filament and said grid electrode, a tuned output circuit connected between said filament and said anode, said output circuit including a network provided with an in anode, acondenser connected between the 30' ductance, at least a portion of said inductancebeing connected between said anode and said filament, a condenser connected be-- tween said grid electrode and said anode,

and a second condenser connected to said input circuit and to saidinduc'tance;

- 4, A high-frequency amplifier including a plurality of thermionic valves in cascade arrangement,.each valve having a grid electrode and an anode, a, grld c rcult and an anode circuit, and an inductance coil connected in each anode circuit, one terminal of said coil being connected to the anode of its-respective valve, an intermediate point of said coil being connected through a hightension battery to the filament circuit, the

other terminal of said coil being connected through a capacity to the grid electrode of 5 the same valve and through another capacity to the grid circdit of the next succeeding valve. y 5. A high-frequency amplifier including, a plurality of thermionic valves in cascade arrangement each valve having a grid elec trode and an anode, a'gridcircuit and'an anode circuit, an inductance coil in each anode circuit, one terminal of said inductance coil being connected to the anode of '60 its respective valve, the midpoint of said coil being connected through a high-tensionbattery to the filament circuit, the other terminal being connectedthrough a capacity 4 to the grid electrode of the same valve and .65 through another capacity to the grid circuit of the next succeedingvalve, a condenser connected, across the terminals of said coil and adjustable to tune the same, and a second condenser connected across the anode and the grid electrode of said first-mentionedvalve to supplement the natural interelectrode capacity thereof,

6. In a radio receiver, a series of thermionic valves in cascade arrangement, each of said thermionic valves being provided with a grid electrode and an anode, an input circuit terminating in each grid elec-- trode, an out-put circuit terminating in each input circuit and the out-put circuit of each valve to supplement the inherent capacity thereof, means for neutralizing said inherent capacities and the capacities of said first mentioned condensers, a condenser coupling 5 the out-put circuit of one thermionic'valve" r to an in ut circuit of a second thermionic valve, a etectorelectrically associated with said'second thermionic valve, said detector being pr vided with input and out-put circuits, an a condenser connecting the 'd of one of said amplifying thermionic va ves to the input circuit 0 said detector.

JOHN SCOTT TAGGART. 

